Finding affordable PCIe options for sound aficionados.

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For years, we've trumpeted the benefits of discrete sound cards. They simply sound better than the typical integrated audio on motherboards, especially for those with discerning ears and halfway-decent speakers or headphones. Good sound cards tend to last through multiple upgrade cycles, too. They're amazingly inexpensive considering the expected lifespan. Indeed, the two we'll be putting under the microscope today—Asus' Xonar DGX and DSX—sell for less than $50.

If the names look familiar, that's because the cards are the PCI Express versions of the Xonar DG and DS. Those older models have PCI interfaces, like an awful lot of other sound cards, and PCI slots are quickly disappearing from modern motherboards. The Xonar DGX and DSX drop into any PCIe x1 slot, and those should be with us for a good, long time.

Each card has a unique character. The DGX courts headphone users with a dedicated amplifier and Dolby Headphone surround-sound virtualization. Meanwhile, the DSX offers home-theater users a replaceable OPAMP, support for more output channels, and the ability to encode multichannel digital bitstreams in real-time.

How do the two compare, and more importantly, how good do they sound? We've conducted a mix of performance, signal quality, and blind listening tests to find out. We've also thrown in our favorite mid-range sound card, the Xonar DX, and a motherboard with Realtek's latest audio codec. This should be interesting.

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Before we dig into the Xonars, it's worth taking a moment to expand on why sound cards tend to last so long. To be frank, the market for them has largely stagnated.

Games used to drive the demand for hardware-accelerated audio, but that feature has all but disappeared from recent titles. Creative's EAX positional audio scheme died years ago. OpenAL was supposed to be a replacement of sorts, but Creative's list of games with OpenAL audio hasn't been updated since 2008. Blue Ripple Sound's Rapture3D positional audio software is used by some Codemasters games, and it's been made to work with a handful of OpenAL titles. However, Blue Ripple Sound is quite explicit about the fact that its algorithms run on the CPU.

The fact is today's multi-core processors have an abundance of horsepower. Crunching numbers for positional audio shouldn't be a challenge. These days, developers typically handle positional audio processing in software. Some, like Battlefield 3 maker DICE, even offer their own virtualization voodoo.

Perhaps because the need for hardware acceleration has waned, the flow of new audio processors has slowed to a trickle. We've had plenty of output channels and real-time encoding options for quite some time, leaving few reasons for fresh silicon.

The older audio processors that dominate the market are designed for the PCI interface, which is quickly falling out of favor among motherboard makers. Intel dropped PCI support from its consumer desktop platforms years ago, forcing board makers to employ third-party silicon if they want to offer PCI slots. Most still do, but it probably won't be long before the majority of new boards are PCIe-only.

Since the C-Media audio processors used in the Xonar line lack native PCIe support, Asus has taken to using bridge chips to link up with the newer interface. The DGX and DSX both feature PLX's PEX8112 bridge chip, just like the other PCIe members of the ever-growing Xonar family. Bridged solutions aren't quite as slick as native ones, of course, but we've yet to see any issues related to Asus' use of the PLX chips.

In the picture above, you can see the bridge chip next to C-Media's Oxygen HD CMI8786 audio processor on the Xonar DGX. That's the same C-Media chip as on the older DG model. Likewise, the DSX features the same Asus AV66 audio processor as the Xonar DS. Though Asus' name is silkscreened on the surface, the AV66 is actually a C-Media CMI8788. Asus tells us the AV66, AV100, and AV200 processors featured on its Xonar cards are all variants of the CMI8788 with different software packages.

We're at a loss as to why Asus doesn't have its own name branded across the CMI8786. That chip is a custom order just for the Xonar DG and DGX. The CMI8786 is really just a cut-down version of the CMI8788. Both chips can handle 24-bit audio, but the CMI8788 does so at sampling rates up to 192kHz, while the CMI8786 tops out at 96kHz.

As the model numbers suggest, the CMI8788 can feed eight output channels, while the CMI8786 is capped at six. Translation: the Xonar DSX can power 7.1-speaker home theaters, while the DGX is limited to 5.1-speaker setups.

Asus uses a different mix of complementary digital-to-analog and analog-to-digital conversion silicon on each card. The DSX pairs a six-channel Wolfson DAC with a stereo codec from the same company. Cirrus logic supplies the conversion hardware for the DGX, which uses a similar DAC-and-codec combo. Incidentally, all of the DAC and codec chips offer 24 bits of resolution at 192kHz sampling rates. The Xonar DGX's 96kHz limitation comes from its audio processor alone.

The published signal-to-noise ratios of each card give us a general sense of their overall signal quality. Looks like the Xonar DGX might be the more balanced of the two; it has a 105-decibel output SNR and a 103-dB input SNR. The DSX has higher output SNR, at 107 dB, but its 100 dB input SNR is a little low.

The Xonar DGX is the less expensive of the two cards, but by less than the cost of a super-sized McDonald's combo. Deciding between the two may be more a factor of whether you intend to hook up the card to a fancy home-theater receiver or run it through a headset or headphones. We'll explore the features tailored to each setup as we take a closer look at each card.